A type of semiconductor element in which a conductive path is provided in the longitudinal direction of the element in order to cope with high voltage or a large amount of current is generally referred to as a “power semiconductor element” (for example, an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a bipolar transistor, a diode, or the like). A semiconductor device having a power semiconductor element mounted on a circuit board and packaged using a sealing resin has been used in a wide range of fields such as industrial devices, vehicles, and railways. In recent years, as the performance of an apparatus including such a semiconductor device becomes higher, the semiconductor device has been required to attain higher performance such as increased rated voltage and rated current, an increased operating temperature range (higher and lower temperatures), and the like.
A structure called “case structure” is mainly used for the package structure of the semiconductor device. The case type semiconductor device has such a structure that a power semiconductor element is mounted on a base plate for heat radiation with an insulating substrate being interposed therebetween and a case is adhered to the base plate. A power semiconductor element mounted inside the semiconductor device is connected to a main electrode. A bonding wire is used for the connection between the power semiconductor element and the main electrode. Generally, as a sealing resin for the semiconductor device, an insulating gel filler such as a silicone gel is used in order to prevent insulation failure under application of high voltage.
In a conventional semiconductor device, there is disclosed a semiconductor device having a structure with a holding cover inserted in close contact with the upper surface of a silicone gel in order to prevent a bonding wire from being disconnected by movement of the silicone gel, wherein the holding cover has a side surface that is provided with a protrusion engaged with the inner wall of an outer case so as to be movable upward and downward (for example, Patent Document 1).
Moreover, in addition to this, there is disclosed a semiconductor device having a structure including a cover portion that covers the upper surface of silicone gel and that has an end portion fixed to a case, wherein at least 80% of the upper surface of the silicone gel is in contact with the cover portion in a temperature range in which use thereof is permitted (for example, Patent Document 2).